Wavelength division multiplexing (WDM) has been used in optical network communications systems and other applications. Essentially, different wavelengths of light would be used to carry information down one or more optical fibers. A WDM multiplexer would be used to couple the different wavelengths into a single fiber. Similarly, WDM demultiplexers are used to separate one or more wavelengths from the fiber. See Buckman, Lisa A. et al., “Demonstration of a Small-Form-Factor WWDM Transceiver Module for 10-Gb/s Local Area Networks,” IEEE Photonics Technology Letters, Vol. 14., No. 5., p. 702-704, May 2002, and/or Lemoff, B. E. et al., “Zigzag waveguide demultiplexer for multimode WDM LAN,” Electronic Letters, Vol. 34, No. 10, p. 1014-1016, May 14, 1998, the disclosures of which are hereby incorporated herein by reference.
Parallel optics and wavelength division multiplexing (WDM) are two optical communication techniques that permit increased bandwidth density in optical communications systems. In parallel optics, multiple optical signals are transmitted in parallel along a multioptical fiber ribbon, with a single optical signal being transmitted on each optical fiber. In WDM, multiple optical data signals are combined and transmitted on a single optical fiber, with each optical signal being carried on a different wavelength. In parallel WDM (PWDM), the two techniques are combined by transmitting multiple optical wavelengths through each optical fiber of a parallel optical fiber ribbon. A key component of a PWDM system is a PWDM multiplexer, an optical device that combines multiple optical beams into a single optical fiber.
In some implementations of PWDM, the optical transmitter includes an array of vertical cavity surface emitting lasers (VCSELs). The number of VCSELs in the array is typically equal to the number of optical fibers in the optical fiber ribbon multiplied by the number of wavelengths in each optical fiber. The optical multiplexer serves to couple light from one VCSEL into one optical fiber in the optical fiber ribbon. Typical multiplexers use wavelength selective means such as dielectric interference filters or diffraction gratings to accomplish this.